"I was struck by how brutally true and honest the writing was," Ewan McGregor said. "Then I found it was a true story and that some of those lines of dialogue were what the family remembered saying."
The film in question, The Impossible, tells the incredible survival story of a tourist family during the South Asian tsunami of 2004.
McGregor and his co-stars were at TIFF on Sunday night not only to celebrate the film's debut – but also to honour all of the victims who suffered from the disaster. (The family was also at the premiere, though not doing press.)
"There is a lot suffering in the story, so we had a great deal of responsibility," said director J.A. Bayona, who also directed The Orphanage. "I mean, the emotions that we were dealing with were real emotions."
Some have criticized the film for focusing on one family's survival instead of the hundreds of thousands of people who were killed.
To that, Bayona said: "We were very aware from the beginning that while we were going to tell this story of one family, we were also going to tell the story of all the people around them. There is a lot suffering in survival."
The gravity wasn't lost on the stars, either.
"It's a delicate subject but an important one," Naomi Watts said. "These people continue to be impacted by this day."
Watts plays the mother of the family. She (SPOILER ALERT!) gets stranded with her eldest son, played by Tom Holland, separated from her husband and other two children.
Holland, 16, also understood the sensitivity of his first major movie.
"I met a lot of survivors," he said. "It was amazing to speak to them."
Despite the seriousness of the topic, Holland's red carpet experience wasn't all doom and gloom. He did get some voracious cheers from the crowd outside the Princess of Wales theatre.
"It was madness," he said with a grin. "I've never had anything like this happen to me before."